Tearing resistance of heterogeneous welds in Single Edge notched Tensile (SE(T)) testing

Abstract

Understanding the behavior of a defect in a welded structure subjected to loading is an important aspect of its integrity assessment. Additionally, local strength and toughness variations (heterogeneity) present within a weld region complicate the assessment. Single specimen Single Edge notched Tension (SE(T)) testing has become a mainstream method to characterize the ductile tearing resistance of metals under conditions of low crack tip constraint. The post-processing of single specimen SE(T) test results requires calculation of crack driving force and crack extension as the test progresses. Various methods have been investigated and were shown to be reliable for testing of homogeneous materials. Published data, however, indicate that the accuracy of these methods may degrade when testing welded joints. This paper reports on an SE(T) test program in which several weld configurations (including severely heterogeneous welds) were tested. Direct Current Potential Drop (DCPD) method is adopted to assess the crack extension and is compared with the Normalization Data Reduction (NDR) technique and nine point method. Based on the results, it can be observed that DCPD is a robust technique to understand the crack behavior in the heterogeneous region as it indicates the variations in resistance curves and is also an effective method to predict final crack extension. The NDR method, albeit more straightforward to apply, does not reveal the irregular shape of tearing resistance curves observed for heterogeneous welds. In presence of crack path deviation, DCPD analysis is related to crack extension projected in the through-thickness direction, rather than the extension along its actual trajectory.